Mode S
 

Surely Mode S equipment is cheep enough for ALL aircraft to be equipped with it, especially if they are operating in crowded airspace such as the South East of England.

I regularly hear and sometimes see aircraft flying near me including those powered by Merlin engines and not showing up on FR24 or ADS B Exchange. The Merlin engined ones are almost certainly operating out of Biggin Hill and headed to Beach Head.

Why??? The Mk 1 Eyeball is not infallible.

The Biggin Spitfires sometimes show up, sometimes not. Haven't seen much of the P-51 though it does occasionally appear on ADSB. No idea if the TP-40 is flying yet...

Almost all aircraft nowadays are already equipped with Mode S (those Spitfires included).

But Mode S on its own isn't usually sufficient for an aircraft to be plotted on the flight trackers (unless they are capable of multilateration). I suspect you are really talking about ADS-B, which is a different issue.

FR24 or ADS-B Exchange both use MLAT (multilateration) but this requires four or more groundstations receiving a steady Mode S signal, so a good ground-receiver coverage and, depending on the terrain, an aircraft altitude of a (few) thousand ft at minimum, is required.
With 'ADS-B Out' in the aircraft sending the GPS position, only 1 ground-receiver is needed. But this makes the onboard equipement a lot more expensive. And more complicated to install on historical aircraft...

Quick look round the markets shows about £2000 for a light aircraft mode S box and up to £7500 for more sophisticated kit. Knowing the tight budgets of some of my flying buddies I reckon they are a few years away from swapping out their trusty KT76A mode C jobs...

PS Loved the mistyped "cheep" in a thread about " Squawking" :ok:

Or, more accurately, "squittering". Best not go there. :O

I just had to go somewhere else with that...

Incidentally, Biggin's Mustang was briefly visible yesterday on ADSB-Ex, I didn't see where it went